Modulatable nozzle system

ABSTRACT

Apparatus generally includes a convergent-divergent outer nozzle duct and a dual cone nozzle plug within and coaxial with the duct and serving as an inner nozzle duct defining with the outer duct a variable area flow path of annular cross section. Forward cone section extends forward from plane of throat of outer duct and aft cone extension extends rearward from throat plane to exit plane. Nose cone forward of dual cones streamlines entire plug. Both cone sections are made up of elongate peripherally overlapping petals with aft ends of forward petals pivoted to forward end of aft petals. Forward ends of forward petals are pivoted to mounting ring on central coaxial support member. Aft ends of forward petals are pivoted to support struts which are pivoted to axially moving second mounting ring to expand and contract both cones at throat plane. Aft ends of aft petals are pivotally connected to actuating struts which are pivotally connected to sleeve which slides axially on support member to expand and contract aft end of aft cone independently of expansion and contraction at throat plane. Support member is hollow, and air supplied to it from external source flows to and through the petals and the forward tip of the nose cone to cool the parts exposed to the hot exhaust gases.

United States Patent [72] Inventor Richard H. Timms San Diego, Calif.[21] Appl. No. 52,210 [22] Filed July 6, 1970 [45] Patented Oct. 12,1971 [73] Assignee Rohr Corporation Chula Vista, Calif.

[54] MODULATABLE NOZZLE SYSTEM 12 Claims, 7 Drawing Figs.

[52] [1.8. Ci 239/l27.3, 239/265. 1 9 [51] Int. Cl 864d 33/04 [50] Fieldof Search 239/l 27.3, 26519, 265.11; 60/271 [56] References Cited UNITEDSTATES PATENTS 3,237,864 3/1966 Taylor et al.... 2319/1273 3,39l,8697/1968 Glass 239/265.19

Primary Examiner-M. Henson Wood, Jr. Assistant Examiner-lohn .l LoveAttorneyGeorge E. Pearson ABSTRACT: Apparatus generally includes aconvergentdivergent outer nozzle duct and a dual cone nozzle plug withinand coaxial with the duct and serving as an inner nozzle duct definingwith the outer duct a variable area flow path of annular cross section.Forward cone section extends forward from plane of throat of outer ductand aft cone extension extends rearward from throat plane to exit plane.Nose cone forward of dual cones streamlines entire plug. Both conesections are made up of elongate peripherally overlapping petals withaft ends of forward petals pivoted to forward end of aft petals. Forwardends of forward petals are pivoted to mounting ring on central coaxialsupport member. Aft ends of forward petals are pivoted to support strutswhich are pivoted to axially moving second mounting ring to expand] andcontract both cones at throat plane. Aft ends of aft petalls arepivotally connected to actuating struts which are pivotally connected tosleeve which slides axially on support member to expand and contract aftend of aft cone independently of expansion and contraction at throatplane. Support member is hollow, and air supplied to it from externalsource flows to and through the petals and the forward tip of the nosecone to cool the parts exposed to the hot exhaust gases.

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ATTORNEY PATENTED 0m 1 2 l97i SHEET 3 BF 3 INVENTOR. RICHARD H. TIMMSATTORNEY MODULATABLE NOZZLE SYSTEM BACKGROUND OF THE INVENTION Thisinvention lies in the field of gas turbine engines, commonly called jetengines which produce reaction thrust by ejecting a high velocity streamof gas from the exhaust nozzle of the gas turbine, and is directed toapparatus for varying the area or profile of the nozzle to achieveoptimum operating conditions for varying flight regimes.

The patent to Benjamin G. Glass, U.S. Pat. No. 3,391,869, issued July 9,I968, explains in detail the various flight conditions of jet-enginedairplanes and the nozzle configuration best suited for each condition.In general, it is pointed out that a convergent nozzle is suited forsubsonic and low supersonic flight while a convergent-divergent nozzleis required for very high speeds such as Mach 1.5 or higher. Thus, anairplane which is intended for operation over substantial periods oftime at speeds in these various ranges requires a nozzle with a variableprofile.

The Glass Patent discloses a nozzle having a dual cone nozzle plugmounted coaxially therein, and which can be adjusted throughout a widerange of profiles to achieve high thrust efficiency under widely varyingoperating conditions. However, the apparatus for expanding andcontracting the cones is rather complicated, is subject to vibration,and includes many small components which are subject to wear and failureand are difficult to repair.

My copending U.S. Pat. application, Ser. No. 887,061, filed Dec. 22,1969, is based on a thrust-modulating plug structure with improvedactuation of the aft ends of the petals of the forward section, the aftends of the petals of the aft section being nonexpansible.

SUMMARY OF THE INVENTION The presentinvention provides a dual conenozzle plug of the same general configuration as the plug disclosed inthe Glms patent, and my pending application, either of which may be usedwith the same outer nozzle duct or with other outer nozzle ducts. Theapparatus for actuating the cones of the present application isrelatively simple in design and provides superior rigidity anddurability with low maintenance costs, and it is provided with means tosupply adequate cooling air to every component which is subjected to theheat of the exhaust gases.

Generally stated, the apparatus comprises an elongate hollow supportmember which is adapted to be mounted coaxially in an outer nozzle ductand may be rigidly secured in place by one or more radial strutsextending from a forward portion of the support member to the wall ofthe outer nozzle duct. The struts may be hollow to serve as flow pathsfor cooling air supplied by a bypass duct, compressor bleed, or thelike.

The dual cones surround and are supported by the intermediate and aftportions of the support member, while the forward portion is preferablyformed as a tapered nose cone to divide the exhaust gases and cause themto flow smoothly over the cones. Each cone is made up of a plurality ofslender elongate leaves or petals which are arranged in peripherallyoverlapping sliding relation. The forward ends of the forward petals arepivotally connected to a first mounting ring on the support member andtheir aft ends are pivotally connected to a plurality of support strutswhich in turn are pivotally connected at their inner ends to a second,axially sliding, mounting ring. The axial movement of this ring causesthe aft ends of the forward petals to expand and contract. In order toproduce a straight line motion with the aft ends of the petals in acommon plane perpendicular to the axis of the support member, aplurality of guide struts may be pivoted at their inner ends to a third,fixed, mounting ring and pivotally connected at their outer ends tointermediate points on the support struts. This construction itparticularly desirable when the aft ends of the petals must bemaintained precisely in the plane of the throat of an outer nozzle duct.

The forward ends of the aft petals are pivotally connected to the aftends of the forward petals to expand and contract with them and maintaina smooth contour. The aft ends of the aft petals are pivotally connectedto the outerends of a plurality of actuating struts, the inner ends ofwhich are pivotally connected to a sleeve which slides axially on thesupport member to cause the aft ends of the aft petals to expand andcontract in the general plane of the exit end of an outer nozzle duct.In the presently preferred form, a pair of drive motors are housed inthe nose cone portion of the support member, and are drivingly connectedto the sleeve and to the second mounting ring to cause their axialmovement and the expansion and contraction of the intermediate and aftends of the dual cone.

Cooling air from a selected source enters through a hollow strut intothe forward portion of the support member and flows through the memberand a plurality of articulated conduits to the joints between theforward and aft petals. Each petal is formed on its inner face with agenerally axially directed hollow stiffener which communicates at thejoint with the associated conduit to deliver cooling air along thelength of the petal. The petals are preferably hollow with a porousouter wall to provide transpiration cooling. The nose cone is formedwith a double wall having a forward inlet for flow of cooling airadjacent to its outer wall and the forward tip of the cone is aperturedfor further transpiration cooling.

It will be apparent that the apparatus disclosed herein is simple andrugged and that ample cooling of the components is supplied to insurelong service life.

BRIEF DESCRIPTION OF THE DRAWINGS Various other advantages and featuresof novelty will become apparent as the description proceeds inconjunction with the accompanying drawings, in which:

FIG. 11 is a diagrammatic profile view showing the dual cone surfaces inretracted and expanded positions in association with aconvergent-divergent outer nozzle duct;

FIG. 2a is a side-elevational view, partly in section, of the forwardportion of a nozzle plug incorporating the invention;

FIG. 2b is a view similar to FIG. 2a showing the aft portion of theplug;

FIG. 3 is a partial schematic View looking inward at the aft end of theplug;

FIG. 4 is a sectional view taken on line 4-4 of FIG. 21;;

FIG. 5 is a sectional view taken along line 5-5 of FIG. 2a; and

FIG. 6 is an enlarged sectional view taken on line 6-6 of FIG. 2b.

DESCRIPTION OF PREFERRED EMBODIMENT The general arrangement of the dualcone nozzle plug in its relation to the outer nozzle duct and otherassociated parts is schematically illustrated in FIG. I, in which theouter nozzle duct 10 is connected at 12 to the tailpipe 14 of a jetengine, not shown, and a nacelle I6 surrounds the engine and the majorpart of duct 10, terminating slightly forward of the exit end 18. Duct10 comprises a divergent forward section 20, a convergent section 22, athroat 24, and a divergent section 26 terminating at the exit edge 18,and may be shaped as here shown or may have the reentrant curve of a DeLaval type nozzle as shown in FIG. I of the Glass patent.

The nozzle plug 28 comprises a coaxial support member having a forwardsection formed as a tapered nose cone 30 rigidly mounted in place byradial struts 32 which are secured to the wall of section 20 of duct 10,and a centrally located rearwardly directed extension, not shown, whichsupports the forward and aft cones 34 and 36 as well 'as various othercomponents. Plug 28 in its entirety serves as an inner nozzle duct whichcooperates with the outer duct to define a flow path for the exhaustgases, which path varies in area from point to point but is generallyannular in cross section. The pointed nose cone divides the gases andcauses them to flow smoothly over the dual cones 34 and 36. These twocones are so located that they meet in the plane of throat 24 and areexpandable together in that plane. In addition the aft end of cone 36 isexpandable in the general plane of exit 18. In the solid line positionthe net profile of the nozzle is convergent-divergent. In the dottedline position the nozzle is still convergent-divergent but substantiallyaltered for performance in a different flight regime. The phantom lineshowing of cone 36 converts the nozzle to all convergent for stillanother flight regime.

The construction and arrangement of the various elements and componentsmaking up the expandable-contractible plug 28 are shown in detail inFIGS. 2a and 2b. The nose cone 30 constitutes a fairing for the forwardportion 38 of the coaxial support member 40 and, as will be seen, thehollow struts 32 are secured to both portion 38 and the nose cone andprovide flow paths to deliver to portion 38 cooling air supplied by thenacelle or some component of the engine. A reduced diameter portion 42of the support member is secured to portion 38 and extends rearwardlythrough the intermediate portion of the plug, and a further reducedportion 44 is an elongate tube which is secured to portion 42 andextends to the aft end of the plug, where cone 46 is secured to it tostreamline the plug.

As previously pointed out, each of the cones 34 and 36 is composed of aplurality of elongate petals arranged in peripherally overlappingsliding engagement. As seen in FIG. 2b, the two cones meet at a commonplane which is preferably the plane of the throat of aconvergent-divergent nozzle. Cone 34 includes petals 48, each of whichis pivotally connected at 50 to a first mounting ring 52 carried forlimited axial sliding movement on portion 38 of the support member. Thusthe forward end of the cone is of constant diameter and the petals swingout in radial planes to increase the cone angle from apex to base whiletheir side edges 54 remain in overlapped relation at all stages ofexpansion, as will be seen in FIG. 5, to seal the cone against ingressof exhaust gases.

The expanding and contracting movement of the aft ends of petals 48 iseffectuated by a plurality of support struts 56, one for each petal, theouter ends of the struts being pivotally connected at 58 to the petalsand the inner ends being pivotally connected at 60 to a second mountingring 62. This ring is axially slidably mounted on the aft section ofportion 42 of the support member. When ring 62 is fully forward, struts56 hold petals 48 and cone 34 out in the solid line position whichrepresents the maximum degree of expansion. When ring 62 moves fullyrearward it pulls the petals and cone in to the broken line positionwhich represents the maximum degree of contraction. If the firstmounting ring 52 were fixed and there were no other restraint on struts56, then pivots 58 would swing in an arc and leave the throat plane ofthe outer nozzle duct. To achieve the desired straight line planarmotion, a plurality of guide struts 64 are pivotally mounted at theinner ends at 66 to a third mounting ring 68 which is fixed on portion42 and their outer ends are pivotally connected at 70 to intermediatepoints on struts 56. Proper selection of dimensions' will produce truestraight line or planar motion. The foreshortening effect on the cone isaccommodated by a small axial movement of first mounting ring 52.

The'aft cone 36 comprises a plurality of petals 72, the forward ends ofwhich are pivotally connected at 58 to petals 48 and to struts 56 toexpand and contract in unison with them. The 3-way pivotal connection isillustrated in FIG. 4, where it will also'be seen that the forward endsof petals 72 are sub stantially identical in cross section to the aftends of petals 48, including side edges 74 which remain in overlappingrelation throughout expansion and contraction. Expansion and contraction of the aft end of cone 36 is accomplished by means of a slenderelongate sleeve 76 axially slidably mounted on sup port tube 44 and aplurality of actuator struts 78, one for each petal, which are pivotallyconnected at 80 to the sleeve and at 82 to the aft ends of petals 72.With the sleeve in full aft position the struts and petals are in thesolid line position which represents the maximum degree of expansion.When the sleeve moves to full forward position the struts and petals arein the broken line position which represents the maximum degree ofcontraction.

Since the degree of expansion and contraction is so much greater at theaft end of cone 36 than at the forward end, it is necessary to graduallyincrease the curvature of each individual petal toward the rear to allowproper nesting in fully contracted position. Thus the aft ends of petals72 have the much greater curvature shown in FIG. 3, where it can be seenthat they nest snugly in their contracted position and present adaisylike appearance when fully expanded.

Since the aft ends of petals 72 reach a point of minimum overlap it isnecessary to take extra precautions to prevent separation or fluttering.To this end, actuator struts 78 are not connected midway of the width ofeach petal but rather very close to its one side edge. Thus this edge isvery rigidly held against undesired movement. The opposite edge isprovided with an end flange tip 84 extending radially inward beyond theaft edge of the remainder of the petal. A guide pin 86, such as a RollPin, is fixed in tip 84 and extends a short distance axially forwardover the inner surface of the petal. The tip and pin constitute a hookor channel preventing radial separation of adjacent petals. Thus, in thefull expansion condition shown in solid lines strut 78 supports one edgeof a petal directly and the opposite edge of an adjacent petalindirectly. Circumferential separation of the petal ends is prevented bythe provision of an abutment 88 on each petal to engage pin 86.

The mechanism to actuate the second mounting ring 62 for expansion andcontraction of the midportion of the nozzle plug is shown in FIG. 2b.Ring 62 is provided with a plurality of brackets 90 spaced around itsperiphery. A nut member 92, preferably a ball nut, is fixed to eachbracket and axially aligned to receive a threaded shaft 94 which isrotatably mounted in a bearing bracket 96 which is preferably integralwith the third mounting ring 68. Shaft 94 is held against translation bybracket 96 and planetary gear 98 fixed on the end of the shaft. Ringgear 100 rotates around support member portion 42 on bearing 102 and isprovided with external teeth to engage gear 98 and internal teeth toengage drive gear 104. The latter is fixed on the aft end of drive shaft106 which is mounted in bearing 108. An air motor 110 housed in portion38 of the support member drives shaft 106 through gears 112 and 114. Itwill be apparent that rotation of shaft 106 in the appropriate directionwill drive all of the planetary gears 98 through ring gear 100 to rotatethreaded shafts 94 and move the nut members 92 and the second mountingring 62 axially rearward. Opposite rotation will move the ring forward.

The mechanism to actuate sleeve 76 for expansion of the aft end of cone36 is also shown in FIG. 2b. Sleeve 76 is provided with a track follower116 riding in axial track 118 to prevent rotation. It is also providedwith an external thread to engage within rotatable nut member 120, alsoa ball nut, which is mounted in bearings 122 to rotate around supporttube 44. A boss 124 on the forward end of the nut member is providedwith teeth to engage drive gear 126, fixedly mounted on drive shaft 128which is carried in rear bearing 130. An air motor 132, housed inportion 38 of the support member, drives shaft 128 through gears 134 and136. Rotation of shaft 128 in the appropriate direction will rotate nutmember to move sleeve 76 rearward. Opposite rotation will move thesleeve forward.

The cooling air system includes some source of supply, such as an enginecomponent, to provide air through a conduit system symbolized by conduit138 to the interior of at least one hollow radial strut 32 which holdsthe support member 40 in place and thence into the forward portion 38 ofthe support member. The air flows rearward to the plurality of ports 140and thence through conduits 142 which are connected to the ports by balljoints 144 and are formed of two telescoping lengths of tubing. Eachforward petal 48 is formed with an elongate-combined stiffener and airconduit 146, to the aft end of which is secured a flow fitting 148, andeach conduit 142 is connected to the fitting by a ball joint 150. Airflows through conduit 142 and fitting 148 into stiffener 146 and thencealong the entire length of the petal.

Fitting 148 connects through another ball joint 152, centered on pivot58, with a flow fitting 154 which in turn is connected with anelongate-combined stiffener and air conduit 156 extending along thelength of petal 72 to distribute air therethrough.

FIG. 6 is a typical cross-sectional view of one of the petals 72, thepetals 48 being similar in general construction. It will be seen thatpetal 72 is hollow, having an inner wall 158 and an outer wall 160,while the combined stiffener and conduit 156 opens directly through theinner wall to the interior of the petal to supply air thereto. Wall 160is porous to allow air to seep therethrough for transpiration cooling ofthe outer surface.

Air also flows from strut 32 forward into nose cone 30 where a portionpasses out through apertures 1162 in the extreme tip and another portionpasses rearward between the outer wall of the nose cone and a secondaryinner wall 164 through an inlet 166. The thin film of air applies asubstantial cooling effect to the outer wall of the nose cone which isdirectly subjected to the impact of the hot exhaust gases. It thenpasses rearward inside the sliding seal ring 168, which completes theenclosure of the plug, and finally out through the aft end of the plug.

It will be understood that the servomotors 1110 and 132 may be placed inother locations and connected to ring 62 and sleeve 76 by remote drivemeans.

Having thus described the invention, what is claimed as new and usefuland desired to be secured by US. Letters Patent is:

1. In combination with a jet engine having a tailpipe with a rearwardlydischarging nozzle duct adapted to produce reaction thrust, a doublemodulating plug for varying the discharge area and aerodynamiccharacteristics of the nozzle duct, said plug comprising:

a slender, elongate support member rigidly mounted coaxially within saidnozzle duct,

a forward plug section and an aft plug section mounted coaxially of thesupport member and meeting in a plane intermediate the length of, andperpendicular to the longitudinal axis of, the support member, each ofthe sections comprising a plurality of slender elongate petalsoverlapping each other peripherally in sliding relation,

a first mounting ring mounted for axial movement on a forward portion ofthe support member;

means pivotally connecting the forward end of each petal of the forwardsection to the first mounting ring;

means pivotally connecting the aft end of each petal of the forwardsection to the forward end of a corresponding petal of the aft section;

a second mounting ring mounted for controlled axial adjustment on anintermediate portion of the support member;

a first plurality of support struts, one pivotally connected at theinner end thereof to the second mounting ring and at the outer endthereof to the aft end of each of the petals of the forward section;

first controlled power means for moving the second mounting ring axiallyof the support member to move the outer ends of the first plurality ofsupport struts radially outwardly and inwardly along a planeperpendicular to the axis of the support member to expand and contractthe aft end of the forward section and the forward end of the aftsection,

a third mounting ring mounted for controlled axial adjustment on an aftportion of the support member;

a second plurality of support struts, one pivotally connected at theinnner end thereof to the third mounting ring, and at the outer endthereof to an alt portion of each petal of the aft section, and

second controlled power means for moving the third mounting ring axiallyof the support member independently of the second mounting ring toexpand and contract the aft end of the aft section.

2. A nozzle plug as claimed in claim ll wherein the third mounting ringis an externally threaded member slidable on and keyed to the supportmember to prevent relative rotation therebetween, and is moved axiallyby a nut in threaded engagement therewith and restrained against axialtranslation, said nut being driven rotatively by said second powermeans.

3. A nozzle plug as claimed in claim 2, the forward portion of thesupport member being enlarged and hollow, and the second power meansincluding a drive motor housed within a forward portion of the supportmember, a rotatable drive shaft extending rearward from the drive motorto the nut member, and a gear connection between the drive shaft and thenut member.

4. A nozzle plug as claimed in claim 1 wherein the first power drivemeans comprises a plurality of nut elements fixedly secured to thesecond mounting ring at spaced intervals about its periphery, an equalplurality of externally threaded actuator shafts are similarly spacedabout the periphery of the support member, one of said shafts extendingaxially through each nut element and being restrained against axialtranslation, and means for rotating the shafts in unison.

5. A nozzle plug as claimed in claim 1; the forward portion of thesupport member being enlarged and hollow, one of the power meansincluding a rotatable drive motor housed within the forward portion ofthe support member, a ring gear having internal and external teethsurrounding the support member and rotatably mounted thereon, planetarygears on the actuator shaft engaging the external teeth of the ringgear, a pinion engaging the internal teeth of the ring gear, and arotatable drive shaft extending rearward from the drive motor, thepinion being fixedly mounted on the aft end of the drive shaft.

6. A nozzle plug as claimed in claim 1, the forward portion of thesupport member being enlarged and hollow, means for introducing coolingair into the forward portion, the petals of both sections being providedwith generally axially directed hollow stiffeners on their inner faces,and conduit means for conducting cooling air directly from the forwardportion endwise into the stifieners of each section to protect thepetals against the effects of the hot exhaust gases.

7. A nozzle plug as claimed in claim 6 wherein the hollow stiffenersdistribute cooling air lengthwise along the petals, and communicate withthe outer walls of the petals which are porous to facilitatetranspiration cooling.

8. A nozzle plug as claimed in claim 7 wherein the hollow stiffener ofeach petal of the forward section extends to its pivotal connection withits corresponding petal of the aft section and a single conduit suppliescooling air to each such connection for forward flow through the hollowstiffener of each petal of the forward section and rearward flow throughthe hollow stiffener of the corresponding petal of the aft section.

9. A noule plug as claimed in claim 6 wherein the conduit meanscomprises a plurality of articulated conduits connected between thehollow interior of the support member and the interior of each hollowstiffener adjacent the pivotal connection between a petal of the forwardsection and a corresponding petal of the aft section.

10. A nozzle plug as claimed in claim 6 wherein the forward portion ofthe support member is tapered forwardly to define a nose cone to dividethe rearwardly flowing exhaust gases for smooth flow over the plug,means to supply cooling air to the hollow interior of the nose cone,transpiration openings provided in the extreme forward end of the nosecone, a curtain wall spaced inwardly from the wall of the nose cone todefine a passage therebetween for rearward flow of cooling air along thenose cone wall, the hollow interior of the forward portion communicatingwith the transpiration openings and the forward end of the passage.

llll. A nozzle plug as claimed in claim 10 wherein the means supplyingcooling air to the interior of the forward portion comprises at leastone hollow support strut extending from the nozzle to the support memberand serving as a conduit for such cooling air.

12. A nozzle plug as claimed in claim Ml wherein a plurality ofseparately rotatable actuators are mounted in said forward portion andare drivingly connected one to each of the second and third rings.

1. In combination with a jet engine having a tailpipe with a rearwardlydischarging nozzle duct adapted to produce reaction thrust, a doublemodulating plug for varying the discharge area and aerodynamiccharacteristics of the nozzle duct, said plug comprising: a slender,elongate support member rigidly mounted coaxially within said nozzleduct, a forward plug section and an aft plug section mounted coaxiallyof the support member and meeting in a plane intermediate the length of,and perpendicular to the longitudinal axis of, the support member, eachof the sections comprising a plurality of slender elongate petalsoverlapping each other peripherally in sliding relation, a firstmounting ring mounted for axial movement on a forward portion of thesupport member; means pivotally connecting the forward end of each petalof the forward section to the first mounting ring; means pivotallyconnecting the aft end of each petal of the forward section to theforward end of a corresponding petal of the aft section; a secondmounting ring mounted for controlled axial adjustment on an intermediateportion of the support member; a first plurality of support struts, onepivotally connected at the inner end thereof to the second mounting ringand at the outer end thereof to the aft end of each of the petals of theforward section; first controlled power means for moving the secondmounting ring axially of the support member to move the outer ends ofthe first plurality of support struts radially outwardly and inwardlyalong a plane perpendicular to the axis of the support member to expandand contract the aft end of the forward section and the forward end ofthe aft section, a third mounting ring mounted for controlled axialadjustment on an aft portion of the support member; a second pluralityof support struts, one pivotally connected at the innner end thereof tothe third mounting ring, and at the outer end thereof to an aft portionof each petal of the aft section, and second controlled power means formoving the third mounting ring axially of the support memberindependently of the second mounting ring to expand and contract the aftend of the aft section.
 2. A nozzle plug as claimed in claim 1 whereinthe third mounting ring is an externally threaded member slidable on andkeyed to the support member to prevent relative rotation therebetween,and is moved axially by a nut in threaded engagement therewith andrestrained against axial translation, said nut being driven rotativelyby said second power means.
 3. A nozzle plug as claimed in claim 2, theforward portion of the support member being enlarged and hollow, and thesecond power means including a drive motor housed within a forwardportion of the support member, a rotatable drive shaft extendingrearward from the drive motor to the nut member, and a gear connectionbetween the drive shaft and the nut member.
 4. A nozzle plug as claimedin claim 1 wherein the first power drive means comprises a plurality ofnut elements fixedly secured to the second mounting ring at spacedintervals about its periphery, an equal plurality of externally threadedactuator shafts are similarly spaced about the periphery of the supportmember, one of said shafts extending axially through each nut elementand being restrained against axial translation, and means for rotatingthe shafts in unison.
 5. A nozzle plug as claimed in claim 1; theforward portion of the support member being enlarged and hollow, one ofthe power means including a rotatable drive motor housed within theforward portion of the support member, a ring gear having internal andexternal teeth surrounding the support member and rotatably mountedthereon, planetary gears on the actuator shaft engaging the externalteetH of the ring gear, a pinion engaging the internal teeth of the ringgear, and a rotatable drive shaft extending rearward from the drivemotor, the pinion being fixedly mounted on the aft end of the driveshaft.
 6. A nozzle plug as claimed in claim 1, the forward portion ofthe support member being enlarged and hollow, means for introducingcooling air into the forward portion, the petals of both sections beingprovided with generally axially directed hollow stiffeners on theirinner faces, and conduit means for conducting cooling air directly fromthe forward portion endwise into the stiffeners of each section toprotect the petals against the effects of the hot exhaust gases.
 7. Anozzle plug as claimed in claim 6 wherein the hollow stiffenersdistribute cooling air lengthwise along the petals, and communicate withthe outer walls of the petals which are porous to facilitatetranspiration cooling.
 8. A nozzle plug as claimed in claim 7 whereinthe hollow stiffener of each petal of the forward section extends to itspivotal connection with its corresponding petal of the aft section and asingle conduit supplies cooling air to each such connection for forwardflow through the hollow stiffener of each petal of the forward sectionand rearward flow through the hollow stiffener of the correspondingpetal of the aft section.
 9. A nozzle plug as claimed in claim 6 whereinthe conduit means comprises a plurality of articulated conduitsconnected between the hollow interior of the support member and theinterior of each hollow stiffener adjacent the pivotal connectionbetween a petal of the forward section and a corresponding petal of theaft section.
 10. A nozzle plug as claimed in claim 6 wherein the forwardportion of the support member is tapered forwardly to define a nose coneto divide the rearwardly flowing exhaust gases for smooth flow over theplug, means to supply cooling air to the hollow interior of the nosecone, transpiration openings provided in the extreme forward end of thenose cone, a curtain wall spaced inwardly from the wall of the nose coneto define a passage therebetween for rearward flow of cooling air alongthe nose cone wall, the hollow interior of the forward portioncommunicating with the transpiration openings and the forward end of thepassage.
 11. A nozzle plug as claimed in claim 10 wherein the meanssupplying cooling air to the interior of the forward portion comprisesat least one hollow support strut extending from the nozzle to thesupport member and serving as a conduit for such cooling air.
 12. Anozzle plug as claimed in claim 10 wherein a plurality of separatelyrotatable actuators are mounted in said forward portion and aredrivingly connected one to each of the second and third rings.